2002 YAMAHA WR 426F engine

3 - 45
INSP
ADJ
STEERING HEAD INSPECTION AND ADJUSTMENT
2. Inspect:
Bearing free play
Exist play → Replace.
STEERING HEAD INSPECTION AND
ADJUSTMENT
1. Elevate the front wheel by placing a suit-
able stand under the engine.
2. Check:
Steering shaft
Grasp the bottom of the forks and gen-
tly rock the fork assembly back and
forth.
Free play → Adjust steering head.
3. Check:
Steering smooth action
Turn the handlebar lock to lock.
Unsmooth action → Adjust steering ring
nut.
4. Adjust:
Steering ring nut
Steering ring nut adjustment steps:
Remove the headlight.
Remove the handlebar and handle crown.
Loosen the ring nut 1 using the ring nut
wrench 2.
Ring nut wrench:
YU-33975/90890-01403

3 - 48
INSP
ADJ
ELECTRICAL/SPARK PLUG INSPECTION
EC370000
ELECTRICAL
EC371001
SPARK PLUG INSPECTION
1. Remove:
Spark plug
2. Inspect:
Electrode 1
Wear/damage → Replace.
Insulator color 2
Normal condition is a medium to light
tan color.
Distinctly different color → Check the
engine condition.
NOTE:
When the engine runs for many hours at low
speeds, the spark plug insulator will become
sooty, even if the engine and carburetor are in
good operating condition.
3. Measure:
Plug gap a
Use a wire gauge or thickness gauge.
Out of specification → Re-gap.
Spark plug gap:
0.7 ~ 0.8 mm (0.028 ~ 0.031 in)
4. Clean the plug with a spark plug cleaner
if necessary.
5. Tighten:
Spark plug
NOTE:
Before installing a spark plug, clean the gas-
ket surface and plug surface.
Finger-tighten a the spark plug before torqu-
ing to specification b.
T R..13 Nm (1.3 m · kg, 9.4 ft · lb)

3 - 49
INSP
ADJ
IGNITION TIMING CHECK
IGNITION TIMING CHECK
1. Remove:
Timing plug 1
2. Attach:
Timing light
Inductive tachometer
To the spark plug lead.
3. Check:
Ignition timing
Timing light:
YM-33277-A/90890-03141
Inductive tachometer:
YU-8036-B
Engine tachometer:
90890-03113
Checking steps:
Start the engine and let it warm up. Let the
engine run at the specified speed.
Engine speed:
1,700 ~ 1,900 r/min
Visually check the stationary pointer a is
within the firing range b on the rotor.
Incorrect firing range → Check rotor and
pickup assembly.
4. Install:
Timing plug

ENG
4 - 1
EC400000
ENGINE
EC4R0000
SEAT, FUEL TANK AND SIDE COVERS
Extent of removal:1 Seat removal2 Fuel tank removal
3 Side covers removal4 Headlight removal
Extent of removal Order Part name Q’ty Remarks
Preparation for removalSEAT, FUEL TANK AND SIDE
COVERS REMOVAL
Turn the fuel cock to “OFF”.
Disconnect the fuel hose.
1 Seat 1
2 Air scoop (left and right) 2
3 Fitting band 1 Remove on fuel tank side.
4 Bolt (fuel tank) 2
5 Fuel tank 1
6 Side cover (left) 1
7 Side cover (right) 1
8 Headlight coupler 1
9 Headlight 1
13
4
2
3
SEAT, FUEL TANK AND SIDE COVERS

ENG
4 - 4
RADIATOR
EC450001
RADIATOR
Extent of removal:1 Radiator removal2 Coolant reservoir removal
Extent of removal Order Part name Q’ty Remarks
RADIATOR REMOVAL
Preparation for removal Drain the coolant. Refer to “COOLANT REPLACEMENT”
section in the CHAPTER 3.
Seat, fuel tank and side cover Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Exhaust pipe Refer to “EXHAUST PIPE AND
SILENCER” section.
1 Engine guard (right) 1
2 Panel 2
3 Clamp 8
4 Radiator (right) 1
5 Hose 2 1
6 Hose 3 1
7 Hose 4 1
8 Pipe 2/O-ring 1/1
9 Radiator breather hose 1
10 Radiator (left) 1
1

4 - 6
ENGRADIATOR
EC456000
HANDLING NOTE
WARNING
Do not remove the radiator cap when the
engine and radiator are hot. Scalding hot
fluid and steam may be blown out under
pressure, which could cause serious
injury.
When the engine has cooled, open the radi-
ator cap by the following procedure:
Place a thick rag, like a towel, over the radi-
ator cap, slowly rotate the cap counter-
clockwise to the detent. This procedure
allows any residual pressure to escape.
When the hissing sound has stopped,
press down on the cap while turning coun-
terclockwise and remove it.
EC454000
INSPECTION
EC444100
Radiator
1. Inspect:
Radiator core 1
Obstruction → Blow out with com-
pressed air through rear of the radiator.
Bent fin → Repair/replace.
EC455000
ASSEMBLY AND INSTALLATION
Radiator
1. Install:
Pipe 1 1
Hose 1 2
Pipe 2 3
Hose 3 4
Hose 4 5
2. Install:
Hose 2 1
Radiator (left) 2
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..2 Nm (0.2 m · kg, 1.4 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..2 Nm (0.2 m · kg, 1.4 ft · lb)
T R..2 Nm (0.2 m · kg, 1.4 ft · lb)
T R..2 Nm (0.2 m · kg, 1.4 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)

4 - 11
ENGCARBURETOR
EC466020
HANDLING NOTE
CAUTION:
Do not loosen the screws {TPS (throttle
position sensor)} 1 except when changing
the TPS (throttle position sensor) due to
failure because it will cause a drop in
engine performance.
REMOVAL POINTS
Pilot screw
1. Remove:
Pilot screw 1
NOTE:
To optimize the fuel flow at a small throttle
opening, each machine’s pilot screw has been
individually set at the factory. Before removing
the pilot screw, turn it in fully and count the
number of turns. Record this number as the
factory-set number of turns out.
INSPECTION
Carburetor
1. Inspect:
Carburetor body
Contamination → Clean.
NOTE:
Use a petroleum based solvent for cleaning.
Blow out all passages and jets with com-
pressed air.
Never use a wire.

ENG
4 - 22
CAMSHAFTS
CAMSHAFTS
CYLINDER HEAD COVER
Extent of removal:1 Cylinder head cover removal
Extent of removal Order Part name Q’ty Remarks
CYLINDER HEAD COVER
REMOVAL
Preparation for removal Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Carburetor Refer to “CARBURETOR” section.
1 Spark plug 1
2 Engine upper bracket (right) 1
3 Engine upper bracket (left) 1
4 Cylinder head breather hose 1
5 Oil tank breather hose 1
6 Bolt (cylinder head cover) 2
7 Cylinder head cover 1
8 Gasket 1
9 Timing chain guide (upper) 1
1